A comparison of methods for quantitation of metabolites in skeletal muscle.

Quantitation of gastrocnemius muscle metabolites in mice was evaluated using three commonly employed descriptors: wet weight, total protein, and total creatine. A fourth previously unreported descriptor, NAD+, was also evaluated. In resting muscle the coefficients of variation were similar when the metabolite data were normalized by any of the four descriptors. However, in tetanically stimulated muscle, normalization by wet weight yielded metabolite levels which were 23-25% lower than the results obtained when the data were normalized by total protein, total creatine, or NAD+.